Add a "fork" of musl as //fusl.

fusl/src/env/setenv.c

Index: fusl/src/env/setenv.c
diff --git a/fusl/src/env/setenv.c b/fusl/src/env/setenv.c
new file mode 100644
index 0000000000000000000000000000000000000000..76e8ee1206e5b5a4111b8c58481932952de6084f
--- /dev/null
+++ b/fusl/src/env/setenv.c
@@ -0,0 +1,30 @@
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+int __putenv(char *s, int a);
+
+int setenv(const char *var, const char *value, int overwrite)
+{
+	char *s;
+	int l1, l2;
+
+	if (!var || !*var || strchr(var, '=')) {
+		errno = EINVAL;
+		return -1;
+	}
+	if (!overwrite && getenv(var)) return 0;
+
+	l1 = strlen(var);
+	l2 = strlen(value);
+	s = malloc(l1+l2+2);
+	if (s) {
+		memcpy(s, var, l1);
+		s[l1] = '=';
+		memcpy(s+l1+1, value, l2);
+		s[l1+l2+1] = 0;
+		if (!__putenv(s, 1)) return 0;
+	}
+	free(s);
+	return -1;
+}